Photo-induced changes in optical properties of As2S3 and As2Se3 films deposited at normal and oblique incidence

Photostructural transformations in amorphous chalcogenide films have been a subject of intensive research so far. In this paper we discuss the changes in the optical properties of typical As-based chalcogenide glasses (As₂S₃ and As₂Se₃) on exposure to ultraviolet (UV) light. An attempt has been made to systematically investigate the optical parameters like extinction coefficient, refractive index and optical bandgap of the films by measuring the same for as-grown and UV-exposed amorphous films of As₂S₃ and As₂Se₃ prepared by vacuum evaporation technique.     

Immersion holography based on amorphous chalcogenide films

A solid immersion holographic method for the recording of refractive index and surface-relief modulated gratings with a period of 0.1–1 μm in amorphous films of chalcogenide semiconductors As₂S₃ and As–S–Se has been developed and studied. The laser immersion interference lithography can be used as a low-cost method for the exposure of large surfaces with regular patterns like subwavelength-gratings and microsieves. The polarization sensitive properties of the subwavelength refractive-index modulated transmission gratings were studied. The possibility to use the amorphous chalcogenide films as a media for holographic recording and storage of information with high density is discussed.     

Investigation of surface activity and photoinduced diffusion of metals in solution deposited amorphous films of As2S3

Surface activity of solution deposited (SD) amorphous films of As₂S₃ has been investigated. Silver and copper are readily deposited on such films from appropriate aqueous ionic solutions. The metals diffuse into the films upon irradiation with energetic photons. Structure and properties of SD films have been investigated using electron microscopy, optical spectroscopy and differential scanning calorimetry. The amorphous films tend to crystallize upon metal diffusion. The stability of amorphous films, the deposition of metals on their active surfaces and the photo-induced diffusion may all be attributed to the presence or production of charged defects in amorphous chalcogenide films.     

Enhancement of photoinduced transformations in amorphous chalcogenide film via surface plasmon resonances

Laser-matter coupling results specific structural changes in amorphous chalcogenide semiconductor layers which originate from electron-hole excitations, defect creation or modification and subsequent atomic motions. These changes can be influenced by plasmon fields. Plasmon enhanced photo-darkening and bleaching, optical recording in thin As_xSe_1 − x films have been demonstrated in this paper, specifically in As₂₀Se₈₀ and As₂Se₃ compositions which revealed the best effects of stimulated expansion or optical darkening respectively due to the He-Ne laser (λ = 633 nm) illumination. Gold nanoparticles deposited on the silica glass substrate and covered by an amorphous chalcogenide film satisfy the conditions of efficient surface plasmon resonance in this spectral region. These experimental results support the importance of localized electric fields in photo-structural transformations of chalcogenide glasses as well as suggest better approaches for improving the performance of these optical recording media.     

AsK-edge EXAFS study of the ternary system Sb2S3–As2S3–Tl2S

The local environment of arsenic atoms in vitreous samples of the system Sb₂S₃–As₂S₃–Tl₂S has been studied by EXAFS at the AsK-edge. The crystalline compound Tl_5.6As₁₅S_25.3 situated within the zone of glass formation of the Sb₂S₃–As₂S_3–Tl₂S phase diagram was used as reference compound in order to derive appropriate phase and amplitude functions. The structure parameters determined were the number of first neighbours N _As–S, the arsenic-sulphur distance, R _As–S, and the Debye-Waller factor, σ_As–S. The influence of the glass-forming antimony sulphide Sb₂S₃ and the glass-modifying thallium sulphide Tl₂S on the As₂S₃ host matrix has been shown. This revised version was published online in November 2006 with corrections to the Cover Date.     

Effect of electric field on photoinduced changes in the optical properties of chalcogenide glassy semiconductors

The influence of an applied electric field on the photoinduced changes in the optical properties of glassy chalcogenide semiconductor films of the (As₂S₃)_x(As₂Se₃)_1?x solid solution system has been studied in thin-layer structures of the following types: metal-semiconductor-metal, metal-semiconductor-insulator-metal, metal-semiconductor-ionic electrode, and metal-semiconductor-insulator-ionic electrode. The ionic electrodes were created on polymer substrates in a xerographic regime. It is established that the applied electric field significantly influences the photoinduced changes in the optical properties of chalcogenide glassy semi-conductors. Possible mechanisms of the observed electrophotoinduced effect are formulated and its potential applications are indicated.     

Limiting of photo induced changes in amorphous chalcogenide/alumino-silicate nanomultilayers

Photo induced changes in amorphous As₂₀Se₈₀/alumino-silicate nanomultilayers (NML) produced by pulsed laser deposition (PLD) method have been studied in this work. The aim was to investigate the photo induced optical and surface relief changes due to the band gap illumination under the size- and hard cover limited conditions. It was observed that the hard cover layer on the surface of the uniform film or alumino-silicate sub-layers in the NML structure influences the photo darkening and restricts surface relief formations in As₂₀Se₈₀ film or in the related NML compared with this effect in a pure chalcogenide layer. The influence of hard layers is supposed to be connected with limiting the free volume formation at the initial stage of the transformation process, which in turn limits the atomic movement and so the surface relief formation.     

Photoinduced Change of Thermophysical Properties of Chalcogenide As<Subscript><Emphasis Type="Bold">2</Emphasis></Subscript>S<Subscript><Emphasis Type="Bold">3</Emphasis></Subscript>Thin Films

The reversible photoinduced change exhibited by amorphous chalcogenide glasses has been extensively studied recently, partly as an interesting subject for fundamental research in the field of disordered solids and partly due to potential applications in optoelectronics such as photoresists, optical memories, optoelectronic circuits, etc. The illumination of many amorphous chalcogenides changes their internal and/or surface structure while preserving their amorphous state. In this study, amorphous arsenic trisulfide (As₂S₃) thin film samples whose thickness is 5 µm were prepared on silicon wafers by thermal evaporation, and their thermal diffusivity and thermal conductivity were measured by photoacoustic spectroscopy and a 3? method, respectively. These measurements were repeated after illumination by an Ar⁺ laser beam whose photon energy E _g is consistent with the energy band gap of As₂S₃. The results show that the thermal diffusivity and thermal conductivity increase by about 50% and 14–15%, respectively, by the photoinduced darkening, and this can be explained by the rearrangement of atoms and thermal expansion of the film.     

An ellipsometric study of relaxation-induced changes in the optical characteristics and structural inhomogeneity of As2S3 glassy thin films

The optical characteristics of thin (～2-μm-thick) films of As₂S₃ chalcogenide glass prepared by thermal deposition in vacuum have been determined from the results of multiangle ellipsometric measurements using He-Ne laser radiation (λ = 0.6328 μm), with allowance for weak absorption in this spectral range. Relaxation-induced changes in the optical properties of both freshly prepared (unannealed) and annealed As₂S₃ films are determined. The possibility of using ellipsometry for the qualitative estimation of the degree of inhomogeneity of the film and its variation in the course of structural transformations during relaxation or under the action of other factors is considered.     

Preparation of mid-IR-active As2S3/ZnS(ZnSe):Cr2+ composites

We have studied novel materials promising for fiber-optic applications: composites in the form of As₂S₃ glass containing Cr²⁺-doped zinc chalcogenide particles. Their dispersion characteristics and optical properties have been investigated in relation to preparation conditions. Process parameters have been found that enable the fabrication of optical fibers possessing luminescence properties.     

Kinetics of laser-induced photodarkening in arsenic based chalcogenide glasses

Photoinduced changes in the optical properties of chalcogenide glass thin films have been studied extensively but usually only permanent changes were recorded through measurements before and after exposure to pump light. To understand the progression of such effects, in this paper we report in situ measurement of transient changes in the optical transmission of amorphous As₂Se₃, As₅Se₅ and As₄Se₃ thin films during their exposure to a He-Ne laser which has photon energy close to the bandgap of the studied compositions. Mathematical expressions are established, which describe accurately both the light intensity and time dependences of photodarkening. The structural origin of the observed changes is discussed briefly.     

Study of the structure of As0.3Se0.2S0.4Ge0.1 chalcogenide glass using the radial distribution function

In the present work, the structure of As_0.3Se_o.3S_0.4Ge_0.1 chalcogenide glass has been studied using the radial distribution function (RDF). Moreover, the effect of annealing temperature on the short range order of this glass has been investigated. The results revealed that the short range order structure of the as-prepared and annealed As_0.3Se_0.2S_0.4Ge_0.1 chalcogenide glass is close to a regular tetrahedron. The medium range order of As_0.3Se_0.4S_0.4Ge_0.1 chalcogenide glass is topology order. The topological structure of the medium range order can be described by the Phillips model. The structure of As_0.3Se_0.2S_0.4Ge_0.1 chalcogenide glass is stable in the annealing temperature range 324–523 K.     

Optical properties of chalcogenide glasses with ion-synthesized copper nanoparticles

Substrates of chalcogenide glassy semiconductors As₂S₃ and Ge_15.8As₂₁S_63.2 are implanted with Cu⁺ ions (energy 40 keV, radiation dose 1.5 × 10¹⁷ ion/cm², fixed current density in the ion beam 1 μA/cm²). The composite layers are analyzed by measuring linear optical transmittance and recording nonlinear optical absorption using the Z-scan technique at 780 nm (probe laser radiation with 150-fs pulses; intensity of 25–100 mW). It is ascertained for the irradiated materials that (1) the linear transmission characteristic of the optical surface plasmon resonance (SPR) band, which indicates the formation of copper nanoparticles in the near-surface region, has emerged and (2) there are simultaneously saturated and two-photon nonlinear absorption types; the latter prevails as the intensity of laser irradiation is increased.     

Amorphous Arsenic Chalcogenide Films Modified Using Rare-Earth Complexes

Thin As₂Se₃ and As₂S₃ films modified by rare-earth complexes with organic ligands were grown by thermal evaporation. The use of rare-earth complexes made it possible to obtain amorphous films containing up to 2 at % rare earths. It was shown using a number of characterization techniques that the complexes were incorporated into the amorphous films without destruction. The absorption spectra of the films indicate that the introduction of the complexes influences their optical characteristics, which is probably associated with changes in the degree of disordering in the amorphous films.     

Optical nonlinearity in glasses: the origin and photo-excitation effects

Linear and nonlinear optical properties in oxide and chalcogenide glasses have been studied comparatively. Applying a semiconductor concept to these glasses, we show that maximal nonlinear refractive-index at optical communication wavelengths is ～10^?4 cm²/GW, which can be obtained in materials with bandgap energy of ～1.6 eV. It is also shown for SiO₂ and As₂S₃ that linear and nonlinear optical excitations induce different photostructural changes, which are attributable to different photo-electronic transition probabilities.     

Elastic properties of As-Sb-Se glasses

Results of measurement of elastic modulii on As-Sb-Se glasses are reported and their composition dependence discussed. The Young’s and the shear modulii lie in the range of 170–210 and 65–80 kb respectively. These values are typical of chalcogenide glasses. For (As, Sb)₄₀Se₆₀ glasses, the modulii increase monotonically with increasing Sb₂Se₃ content. The observed composition dependence of the modulii for the As _x Sb₁₅Se_{85 −x} glasses is examined in terms of the chemically ordered structural units in the glasses.     

Infrared waveguide fabrications with an E-beam evaporated chalcogenide glass film

Chalcogenide glasses have a variety of unique optical properties due to the intrinsic structural flexibility and bonds metastability. They are desirable materials for many applications, such as infrared communication sensors, holographic grating, optical imaging, and ultrafast nonlinear optic devices. Here, we introduce a novel electron-beam evaporation process to deposit the good quality arsenic trisulfide (As₂S₃) films and then the As₂S₃ films were used to fabricate the As₂S₃ waveguides with three approaches. The first method is photoresist lift-off. Because of the restriction of thermal budget of photoresist, the As₂S₃ film must be deposited at the room temperature. The second one is the silicon dioxide lift-off process on sapphire substrates, in which the As₂S₃ film could be evaporated at a high temperature (>180 °C) for better film quality. The third one is the plasma etching process with a metal protective thin layer in the pattern development process.     

Changes in the Short-Range Order of Chalcogenide Glasses upon Crystallization

The crystallization of the chalcogenide glass formers Se, As₂Se₃, and As₂S₃ is studied by x-ray fluorescence analysis (measurements of the relative integrated intensity of the last x-ray emission line). The results demonstrate that the integral parameter R describing the short-range order is larger in the glasses compared to the corresponding crystals. This finding correlates with earlier reports that glass crystallization is accompanied by a decrease in coordination number and also with the assumption that chalcogenide glasses contain hypervalent configurations.     

Preparation and properties of Bi2−x As x S3 thin films by solution-gas interface technique

The solution gas interface technique by which thin films of Bi_2−x As _x S₃ were deposited is described in this paper. The semiconducting properties of the interface grown Bi_2−x As _x S₃ thin films are studied. The optical absorption, dark resistivity and thermoelectric power of the films were studied and results are reported.     

Investigation of interdiffusion in Sb/As2S3 nano-layered structures by high-resolution X-ray photoelectron spectroscopy

The photo-stimulated interdiffusion within chalcogenide based nano-layered structures (NLS) produces large changes in properties, which have potential application in optical pattern recording. The mechanism of these changes is investigated for two NLS consisting of 100 alternate layers of antimony and As₂S₃, but of different relative thicknesses, by high-resolution X-ray photoelectron spectroscopy. The results suggest the formation of Sb-S bonds at the expense of As-S bonds, with a consequent increase in the refractive index but minimal change in thickness. The role of oxygen in photoinduced transformations, especially in the top layers, is characterized and discussed.